“It’s not clear, it’s not concise and it’s not transparent. Nobody knows what a lime green means, but everybody knows what an A means,” said House Education Committee Chairwoman Lisa Posthumus Lyons, an Alto Republican who is expected to start hearings this week on her soon-to-be introduced legislation to switch to letter grades.

Letter grades – implemented in roughly 15 states – seem intuitive on their face since schools are used to evaluating students with letter grades of their own. The tricky part is determining how the rankings are calculated and making sure they are credible.

Indeed, Lyons’ bills would do more than change the performance scorecard from colors to letters. She said she wants to change the formula so that grades “accurately reflect” schools’ quality.

In the 2012-13 scores released in August, some schools were rated red despite being seen as traditionally high-performing, while other schools got green scores despite having no performance data because they were new, according to critics.

Another complaint is that Michigan’s separate top-to-bottom percentile ranking of schools, which is part of its accountability system under a waiver from federal no Child Left Behind requirements, closely correlates with student poverty rates. And others complain that the top-to-bottom list and separate color grades are not aligned, confusing educators and the public.

One goal of the House bills is to eliminate the top-to-bottom ranking and replace it with A-F grades so there is a single system. That does not mean that designations such as “reward,” “priority” and “focus” schools would necessarily go away because they are in the state’s waiver to the U.S. government. But priority schools in the bottom 5 percent and subject to state intervention could be “F” schools. Reward schools in the top 5 percent could be “A” schools.

“We’re not saying it’s letters are better than colors. We’re saying that the thinking that goes into the creation of the letters is what has to be replaced,” said Gary Naeyaert, executive director of the Great Lakes Education Project, a school-choice advocacy group founded by former Republican gubernatorial candidate Dick Devos and his wife Betsy that has given input on the legislation. “There’s a lack of buy-in among the school community because of the convoluted, ultra complex, impossible methodology of the top-to-bottom ranking, which now has consequences for schools.”

Naeyaert criticized the state Education Department’s decision to hold schools accountable for the achievement gap between the top- and bottom-scoring students instead of measuring the gap between specific racial or demographic groups. Education Department officials declined to be interviewed for this story.

Education Trust-Midwest, an education policy and research organization in Royal Oak, also supports an A-F system but says legislators should be careful when revising the “nuts and bolts” of the accountability system. They may be tempted to let schools off the hook if there is blowback about being given a “D” or “F,” said Amber Arellano, the group’s executive director.

“It’s high-stakes work that takes a lot of technical expertise,” she said.

Arellano said the state’s new system is a major improvement over the previous iteration that graded almost all schools as high performers. But parents and educators deserve more coherent information – a single letter grade for every school in the state – to help improve performance, she said.

“When there’s real accountability and real public reporting and it’s meaningful and there are real consequences when schools don’t perform, it creates a lot of discomfort for the education community,” she said. “For the first two or three years, there’s a lot of discomfort. What we have to get better at as a state is being comfortable with the discomfort.”